Note: Descriptions are shown in the official language in which they were submitted.
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The present invention relates to blast furnace stoves having an
external sheet metal case and an inner lining of insulating and refractory
material as well as means providing a gas-tight seal between the gas streams
and the inside surface of the sheet metal case.
As known, the refractory lining of blast furnace stoves is not
gas-tight itself and permits gases containing aggressive media to penetrate
from the interior of the stove to the inside surface of the sheet metal
case and there to condense. Such condensates cause corrosion and in conjunc-
tion with stresses presentin the sheetmetalcase they are responsible for the
phenomenon known as intercrystalline stress corrosion which within a
relatively short time manifests itself by the appearance of cracks and
fractures in the sheet metal case.
The processes which characterise intercrystalline stress corrosion
are explained in detail in the published specification of our German patent
application No. 1955063, published August 12, 1971, and means are also
described for preventing the deposition of corrosive media on the inside
surface of the sheet metal case. According to this specification a second
inner gas-tight case made of metal or of a high temperature synthetic plastics
material and conforming in shape to the external metal case is included in
the lining and stops gases from penetrating the pores and spaces in the lining
and from reaching the external sheet metal case.
However, in practlce it has been found tltat, if carelessly laid,
such a foil can tear and thls may also happen during operation of the stove,
so that the effectiveness of the gas seal may be destroyed.
It is an object of the present invention to improve the gas seal
protecting the inside surface of the sheet metal case of a blast furnace
stove by means which will reliably stand up to rough usage during assembly
and will stand up to service stresses and strains.
According to the invention this is achieved by the provision of
a layer of expanded silica or foamed glass as a gas-tight barrier layer in
direct proximity with the inside surface of the sheet metal case. By
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"expanded silica" is meant foamed silicate material having a structure
of closed pores or small cells which are closed in an air tight manner to
each other.
Foamed glass usually contains very small self-contained airtight
;~ cells or closed pores which cause this material to be completely impervious
to gases and liquids. Moreover, foamed glass is mechancially suitable
strong and itsclosed pores provide it with outstanding insulating properties.
However, its resistance to temperature reversals is comparatively poor so
that foamed glass has not in the past been considered by skilled engineers
for use in plant in which the temperatures fluctuate and change, as in the
- case of blast furnace stoves which are heated during the on-gas stage and
then blown cold when on-wind.
However, tests have shown that provided the foamed glass is used
as a gas-tight layer in direct proximity of the inside surface of the sheet
metal case the thermal stressing of the material by temperature reversals is
within admissable limits if the insulating and refractory material of the
lining is appropriately dimensioned in accordance with thermal as well as
economic considerations.
The proposal according to the present invention enables the gas-
; 20 tight layer to be constructed so that it complieswith the assembly needs
of the lining and can he erected together with the lining using the
conventional tools and aids. It i9 most unlikely that the layer would be
damaged during erection. Consequently, the layer can be relied upon to form
a gas-tight protection before and after the stove is in service, since any
possibly minor differences in expansion of the ad~acent material and
consequent friction can be readily absorbed by the foamed glass layer.
Moreover, the barrier layer of foamed glass can readily stand up to the
pressure fluctuations which occur inside a hot blast stove.
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Yet another proposal according to the invention consists in
coating one rboth sides of the foamed glass layer at least in the region of
the
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joints in the layer with a meta] or plastics foil. An effective gas seal
will thus be provided to counteract any possible gas perviousness of the
jointing mortar. Conveniently joints may also be sealed with a ceramic
material, such as water glass.
The invention may be put into practice in various ways and a number
of embodiments of the invention will be described to illustrate it with
reference to the accompanying drawings in which
Figure 1 is a diagrammatic longitudinal section of a hot blast
furnace r and
Figures 2 to 5 are different forms of construction shown on a
larger scale of the detail marked A in the hot blast stove shown in Figure 1.
Referring to Figure 1 a blast furnace stove is provided with a
sheet metal case 1 and an internal lining 2 of insulating and refractory
material. The combustion chamber 3 communicates under a cupola 4 with the
flues 5 in the checkerwork 6.
Figure 2 shows the provision of a gas-tight layer 7 of foamed glass
placed with one side against the inside surface of the sheet metal case 1
which may have been first provided with a coat of paint or of some other
material. The foamed glass layer 7 is backed by the lining 2.
Unlike Figure 2 a gas-tight foil 8 is interposed in Figure 3
between the inside surface of the sheet metal case 1 and the lay~7 of foamed
glass and, as will be understood from Figure 4, this foil may alternatively
be interposed between the foamed glass layer 7 and the lining 2. Moreover,
a foil 8 may be provided on each side of the foamed glass layer 7 (Figure 5).
The foils 8 consist of a gas-tight metal or plastics and are
primarily intended to cover the joints in the foamed glass layer 7 and hence
to ensure gas tightness of the layer specifically at the joints.
; The checkerwork 6 of the blast furnace stove is al~ernately heated
by the hot gases generated in the combustion chamber 3 and then blown cold
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whilst heating the air for the blast furnace during the on-wind stage. In
both stages gase~ penetrate the lining 2 as far as the foamed glass layer 7
which bars the way to the sheet metal case 1. Should special operating
states occur in which unexpected condensation occurs on the inside of the
layer 7 this would also be prevented from reaching ~he sheet metal case
because the foamed glass is also impervious to liquids. The inside surface
of the sheet metal case is thus protected from attack by agressive substances.
The foamed glass layer is preferably a material supplied by
Pittsburg Corning as FOAMGLAS~ This material can be used in a thickness
from 2.5 to 13 cms and has a density in the range 135 to 155 kg/cubic metre.
The material is a pure borosilicate glass free of inorganic binder
material and can be used at temperatures of up to 430 C. It has essentially
no water absorption capacity, steam permeability, or capilliarity; it resists
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attack by all acids except hydrofluoric acid, and is incombustible.
, It has a coefficient of thermal conductivity of 0.041 - 0.004
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kcal a compressive strength of 5 to 6.5 kp/cm , a buckling strength of
; 4.5 to 5.3 kp/cm , an elasticity of 10~000 to 12,000 kp/cm , a coef,ficient
of expansion of 8.5 x 10 / grd a specific heat of 0.20 kcal/kg grd and a
thermal conductivity of 4.3 x 10 3 cm2/sec.
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